This application addresses broad Challenge Area (14) Stem Cells, and specific Challenge Topic 14-GB-102: Imaging Stem Cell Migration and Differentiation. Congestive heart failure resulting from myocardial infarction and subsequent adverse left ventricular remodeling is a major cause of morbidity, mortality and health care spending in Western nations. Despite advances in the treatment of heart failure, current pharmacologic and mechanical therapies do not resolve the principal underlying issue, which is the death of cardiomyocytes. The limitations of contemporary therapies are further exacerbated by the heart's own limited ability for self-repair. This dilemma has motivated a search for reparative treatments for the heart, and led to the exploration of therapeutic delivery of stem cells to injured myocardium. In animal studies of acute myocardial infarction, delivery of cell preparations such as unfractionated adult bone marrow or marrow-derived mesenchymal stem cells (MSCs) has improved perfusion and indices of ventricular function. The mechanisms of beneficial effect are incompletely understood, partly because methods are limited for serial tracking of stem cell fate after delivery. Recent data favor the hypothesis that paracrine functions of MSCs predominate to facilitate myocardial healing, angiogenesis, endogenous self-repair, and mitigate inflammation. Encouraging pre-clinical results have rapidly led to clinical trials of cell therapy in acute infarction, which has created a critical need for safe, non-invasive, readily available methods for tracking and quantifying stem cells after delivery. Indeed, the optimization of treatment protocols and acquisition of mechanistic insights into therapeutic cell delivery, are linked to the ability to serially track stem cell biodistribution and viability in vivo. Current imaging methods with clinical potential for visualizing stem cells utilize probes for magnetic resonance or nuclear imaging. These have limitations in terms of radiation exposure, spatial resolution, the requirement for genetic modification of stem cells, technical complexity, and resulting impediments to serial imaging. Accordingly, to address this gap in imaging technology, the current research application will develop an ultrasound-based technology for visualizing exogenously delivered stem cells in vivo. Acoustically active gas-filled polymer microbubbles will be developed as contrast agents for ex vivo labeling of MSCs prior to therapeutic delivery. The overall hypothesis to be tested is that MSC uptake of the microbubbles will enable in vivo visualization of stem cell trafficking using clinically available ultrasound scanners. The project will begin with in vitro validation and optimization of microbubble chemistry, testing of acoustic parameters and cytotoxicity;proceed to in vivo proof of concept in small animals;and then apply the imaging technology to a clinically relevant large animal model of MSC therapy. These studies will culminate in the development of a safe, non-invasive, portable, high resolution, in vivo, real time ultrasound method for visualizing therapeutically delivered MSCs. It is anticipated that contrast- enhanced ultrasound imaging of stem cells will play a pivotal role in the evaluation of cell-based therapies for ameliorating the burden of ischemic heart disease and congestive heart failure in human populations. PUBLIC HEALTH RELEVANCE: Cell-based therapies, such as administration of mesenchymal stem cells (MSCs), are a promising new approach to repair the heart after myocardial infarction. Successful implementation of this strategy requires a greater insight into the mechanism by which MSCs confer therapeutic benefit, which in turn requires an understanding of the distribution and fate of MSCs after local or systemic delivery. This proposal aims to develop an ultrasound-based approach for visualizing MSCs that can be used in patients. This new imaging technology may facilitate the clinical application of MSC therapy, which may ultimately decrease death and disability from myocardial infarction and congestive heart failure.